U.S. patent application number 17/179724 was filed with the patent office on 2022-03-03 for magnetic disk device and method of setting data format.
The applicant listed for this patent is Kabushiki Kaisha Toshiba, Toshiba Electronic Devices & Storage Corporation. Invention is credited to Hiroshi Isokawa.
Application Number | 20220066649 17/179724 |
Document ID | / |
Family ID | |
Filed Date | 2022-03-03 |
United States Patent
Application |
20220066649 |
Kind Code |
A1 |
Isokawa; Hiroshi |
March 3, 2022 |
MAGNETIC DISK DEVICE AND METHOD OF SETTING DATA FORMAT
Abstract
According to one embodiment, a magnetic disk device includes a
disk, a head including a read head that reads data from the disk, a
write head that writes data into the disk, and an assist element
that generates energy for improving write performance of the write
head, and a controller that adjusts a degauss condition after a
stop of a write process of the write head, based on a resistance
value of the assist element, and adjusts a data format of the disk
in accordance with the degauss condition, the resistance value
being measured after data is written into the disk, and the write
process having an influence on the resistance value.
Inventors: |
Isokawa; Hiroshi; (Yokohama
Kanagawa, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kabushiki Kaisha Toshiba
Toshiba Electronic Devices & Storage Corporation |
Tokyo
Tokyo |
|
JP
JP |
|
|
Appl. No.: |
17/179724 |
Filed: |
February 19, 2021 |
International
Class: |
G06F 3/06 20060101
G06F003/06 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 27, 2020 |
JP |
2020-143291 |
Claims
1. A magnetic disk device comprising: a disk; a head including a
read head that reads data from the disk, a write head that writes
data into the disk, and an assist element that generates energy for
improving write performance of the write head; and a controller
that adjusts a degauss condition after a stop of a write process of
the write head, based on a resistance value of the assist element,
and adjusts a data format of the disk in accordance with the
degauss condition, the resistance value being measured after data
is written into the disk, and the write process having an influence
on the resistance value.
2. The magnetic disk device according to claim 1, wherein the
degauss condition includes a degauss duration from when the write
process of the write head is stopped until magnetization of the
write head disappears, and a degauss frequency of a recording
current to be supplied to the write head after the write head stops
the write process.
3. The magnetic disk device according to claim 1, wherein the
controller adjusts the degauss condition so that the resistance
value does not fluctuate in a first measurement of the resistance
value.
4. The magnetic disk device according to claim 3, wherein when the
resistance value in the first measurement of the resistance value
is more than a first upper limit value or less than a first lower
limit value, the controller adjusts the degauss condition so that
the resistance value is within a range of the first upper limit
value and the first lower limit value.
5. The magnetic disk device according to claim 2, wherein the
controller adjusts the data format in accordance with the degauss
duration.
6. The magnetic disk device according to claim 5, wherein when the
degauss duration is shorter than a first period, the controller
reduces a first region disposed between user data and servo data of
the disk.
7. The magnetic disk device according to claim 1, wherein the
assist element is a spin torque oscillator.
8. A magnetic disk device comprising: a first disk including a
first surface having first user data, first servo data, and a first
region between the first user data and the first servo data; a
second disk including a second surface having second user data,
second servo data, and a second region that is provided between the
second user data and the second servo data and has a size different
from a size of the first region; a first head including a first
read head that reads data from the first surface, a first write
head that writes data into the first surface, and a first assist
element that generates energy for improving write performance of
the first write head; a second head including a second read head
that reads data from the second surface, a second write head that
writes data into the second surface, and a second assist element
that generates energy for improving write performance of the second
write head; and a controller that sets a second degauss condition
after a stop of a write process of the second write head, the
second degauss condition being different from a first degauss
condition after a stop of the write process of the first write
head.
9. The magnetic disk device according to claim 8, wherein the
controller adjusts the first degauss condition based on a first
resistance value of the first assist element, which is measured
after data is written into the first disk, adjusts a first data
format of the first disk in accordance with the first degauss
condition, adjusts the second degauss condition based on a second
resistance value of the second assist element, which is measured
after data is written in the second disk, and adjusts a second data
format of the second disk in accordance with the second degauss
condition.
10. The magnetic disk device according to claim 9, wherein the
first degauss condition includes a first degauss duration from when
the first write head stops the write process until magnetization of
the first write head disappears, and a first degauss frequency of a
recording current to be supplied to the first write head after the
write process of the first write head is stopped, and the second
degauss condition includes a second degauss duration from when the
second write head stops the write process until magnetization of
the second write head disappears, and a second degauss frequency of
a recording current to be supplied to the second write head after
the write process of the second write head is stopped.
11. The magnetic disk device according to claim 10, wherein the
controller adjusts the first degauss condition so that the first
resistance value does not fluctuate in a first measurement of the
first resistance value, and adjusts the second degauss condition so
that the second resistance value does not fluctuate in a second
measurement of the second resistance value.
12. The magnetic disk device according to claim 11, wherein the
controller adjusts the first degauss condition so that the first
resistance value is within a range of a first upper limit value and
a first lower limit value, when the first resistance value in the
first measurement of the first resistance value is more than the
first upper limit value or less than the first lower limit value,
and adjusts the second degauss condition so that the second
resistance value is within a range of a second upper limit value
and a second lower limit value, when the second resistance value in
the second measurement of the second resistance value is more than
the second upper limit value or less than the second lower limit
value.
13. The magnetic disk device according to claim 10, wherein the
controller adjusts the first data format in accordance with the
first degauss duration, and adjusts the second data format in
accordance with the second degauss duration.
14. A method of setting a data format, which is applied to a
magnetic disk device including a disk, and a head including a read
head that reads data from the disk, a write head that writes data
into the disk, and an assist element that generates energy for
improving write performance of the write head, the method
comprising: adjusting a degauss condition after a stop of a write
process of the write head, based on a resistance value of the
assist element, the resistance value being measured after data is
written into the disk, and the write process having an influence on
the resistance value; and adjusting a data format of the disk in
accordance with the degauss condition.
15. The method of setting a data format according to claim 14,
wherein the degauss condition includes a degauss duration from when
the write process of the write head is stopped until magnetization
of the write head disappears, and a degauss frequency of a
recording current to be supplied to the write head after the write
head stops the write process.
16. The method of setting a data format according to claim 14,
wherein the degauss condition is adjusted so that the resistance
value does not fluctuate in a first measurement of the resistance
value.
17. The method of setting a data format according to claim 16,
wherein when the resistance value in the first measurement of the
resistance value is more than a first upper limit value or less
than a first lower limit value, the degauss condition is adjusted
so that the resistance value is within a range of the first upper
limit value and the first lower limit value.
18. The method of setting a data format according to claim 15,
wherein the data format is adjusted in accordance with the degauss
duration.
19. The method of setting a data format according to claim 18,
wherein when the degauss duration is shorter than a first period, a
first region disposed between user data and servo data of the disk
is reduced.
20. The method of setting a data format according to claim 14,
wherein the assist element is a spin torque oscillator.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from Japanese Patent Application No. 2020-143291, filed
Aug. 27, 2020, the entire contents of which are incorporated herein
by reference.
FIELD
[0002] Embodiments described herein relate generally to a magnetic
disk device and a method of setting a data format.
BACKGROUND
[0003] In order to realize high recording density and high
recording capacity of a magnetic disk device, a microwave assisted
magnetic recording (MAMR) type, a thermally assisted magnetic
recording (TAMR) type, and the like have been developed. The
microwave assisted magnetic recording type is a technique in which
a magnetic head including a recording magnetic pole (main magnetic
pole) and a high-frequency oscillator is used to apply a
high-frequency magnetic field to a disk, and thus the coercive
force of a part of the disk to which the high-frequency magnetic
field is applied is reduced. The recording magnetic pole is excited
by applying a recording current to generate a recording magnetic
field. The high-frequency magnetic field is generated by energizing
the high-frequency oscillator. The thermally assisted magnetic
recording type is a technique in which a magnetic head including a
light irradiation element is used and the disk is locally heated by
irradiating the disk with irradiation light from the tip of the
light irradiation element, and thus the coercive force of a heated
part of the disk is reduced. The light irradiation element
irradiates the disk with the irradiation light.
[0004] In the magnetic disk device, when data write process is
stopped before particular data, a recording current or recording
voltage to be applied to a recording coil is gradually attenuated.
Therefore, residual magnetization is generated in the head 15 by
the recording current or recording voltage. In order not to erase
the data by such residual magnetization, a region such as a gap is
provided immediately before the data in the magnetic disk device.
The formatting efficiency of the disk may decrease by providing
such a gap.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a block diagram illustrating a configuration of a
magnetic disk device according to an embodiment.
[0006] FIG. 2 is a schematic diagram illustrating an example of
disposition of a head with respect to a disk according to the
embodiment.
[0007] FIG. 3 is an enlarged cross-sectional view illustrating an
example of the disk and the head according to the embodiment.
[0008] FIG. 4 is a schematic diagram illustrating an example of a
degauss operation.
[0009] FIG. 5 is a schematic view illustrating an example of a
method of adjusting a degauss condition corresponding to the head
according to the embodiment.
[0010] FIG. 6 is a schematic view illustrating another example of
the method of adjusting the degauss condition corresponding to the
head according to the embodiment.
[0011] FIG. 7 is a schematic view illustrating an example of a
format of a surface of the disk corresponding to the head according
to the embodiment.
[0012] FIG. 8 is a schematic view illustrating an example of a
format of a back surface of the disk corresponding to the head
according to the embodiment.
[0013] FIG. 9 is a flowchart illustrating an example of a method of
setting a data format according to the embodiment.
DETAILED DESCRIPTION
[0014] In general, according to one embodiment, a magnetic disk
device comprises: a disk; a head including a read head that reads
data from the disk, a write head that writes data into the disk,
and an assist element that generates energy for improving write
performance of the write head; and a controller that adjusts a
degauss condition after a stop of a write process of the write
head, based on a resistance value of the assist element, and
adjusts a data format of the disk in accordance with the degauss
condition, the resistance value being measured after data is
written into the disk, and the write process having an influence on
the resistance value.
[0015] Hereinafter, an embodiment will be described with reference
to the drawings. The drawings are examples, and do not limit the
scope of the invention.
Embodiment
[0016] FIG. 1 is a block diagram illustrating a configuration of a
magnetic disk device 1 according to an embodiment.
[0017] The magnetic disk device 1 includes a head disk assembly
(HDA) described later, a driver IC 20, a head amplifier integrated
circuit (hereinafter, head amplifier IC or preamplifier) 30, a
volatile memory 70, a non-volatile memory 80, and a buffer memory
(buffer) 90, and a system controller 130 being an integrated
circuit of one chip. The magnetic disk device 1 is connected to a
host system (simply referred to as a host below) 100.
[0018] The HDA includes a magnetic disk (referred to as a disk
below) 10, a spindle motor (referred to as a SPM below) 12, an arm
13 on which a head 15 is mounted, and a voice coil motor (referred
to as a VCM below) 14. The disk 10 is attached to the SPM 12 and is
rotated by driving the SPM 12. The arm 13 and the VCM 14 form an
actuator. The actuator controls the movement of the head 15 mounted
on the arm 13 to a particular position on the disk 10 by driving
the VCM 14. A plurality of disks 10 and a plurality of heads 15 are
provided. Only a disk 10 and a head 15 may be provided.
[0019] In the disk 10, a user data region 10a which is available to
the user, a media cache 10b (may also be referred to as a media
cache region or a storage region), and a system region 10c are
allocated as regions in which writing of data is possible. Data (or
a command) transferred from the host and the like is temporarily
stored or recorded in the media cache before being written into a
particular region of the user data region 10a. Information required
for system management is written into the system region. In one
example, the storage region (for example, media cache 10b)
corresponds to a cache region for resolving the discrepancy between
a processing speed (at which data is processed in a particular
part) or a transfer rate at which data is transferred from a
particular region to the disk 10, and a write rate at which data is
written into the disk 10. The storage region may include the system
region 10c. The region of the disk 10 other than the media cache
10b and the system region 10c for temporarily storing or recording
data may be used as the storage region. The system region 10c may
include the storage region. A direction from the inner
circumference to the outer circumference of the disk 10 or a
direction from the outer circumference to the inner circumference
of the disk 10 is referred to as a radial direction below. In the
radial direction, the direction from the inner circumference to the
outer circumference is referred to as an outer direction (outside),
and the direction from the outer circumference to the inner
circumference is referred to as the inner direction (inside). A
direction orthogonal to the radial direction of the disk 10 is
referred to as a circumferential direction. The circumferential
direction corresponds to a direction along the circumference of the
disk 10. A particular position in the radial direction of the disk
10 may be referred to as a radial position. A particular position
in the circumferential direction of the disk 10 may be referred to
as a circumferential position. The radial position and the
circumferential position may be collectively and simply referred to
as a position. A "track" means one of a plurality of regions
obtained by division in the radial direction of the disk 10, a path
of the head 15 at a particular radial position, data extending in
the circumferential direction of the disk 10, and data for one lap,
which is written on a track at a particular radial position, and
data written on the track. In addition, the "track" is used with
various meanings. A "sector" means one of a plurality of regions in
which a track is divided in the circumferential direction, data
written at a particular position on the disk 10, and data written
on a sector. In addition, the "sector" is used with various
meanings. The "width of a track in the radial direction" may also
be referred to as a "track width". The "path passing through the
center position of a track width in a particular track" is referred
to as a "track center".
[0020] The head 15 faces the disk 10. For example, a head 15 faces
a surface of the disk 10. The head 15 includes a slider as a main
body, and includes a write head 15W and a read head 15R mounted on
the slider. The write head 15W writes data into the disk 10. The
read head 15R reads data written on the disk 10. In addition, the
"write head 15W" may be simply referred to as the "head 15". The
"read head 15R" may be simply referred to as the "head 15". In
addition, the "write head 15W and read head 15R" may be
collectively referred to as the "head 15". The "center of the head
15" may be referred to as the "head 15". The "center of the write
head 15W" may be referred to as the "write head 15W". In addition,
the "center of the read head 15R" may be referred to as the "read
head 15R". The "center of the write head 15W" may be simply
referred to as the "head 15", and the "center of the read head 15R"
may be simply referred to as the "head 15". "Positioning the center
of the head 15 on the track center of a particular track" may mean
"positioning the head 15 on a particular track", "disposing the
head 15 on a particular track", or "locating the head 15 on a
particular track".
[0021] FIG. 2 is a schematic diagram illustrating an example of
disposition of the head 15 with respect to the disk 10 according to
the present embodiment. As illustrated in FIG. 2, a direction in
which the disk 10 rotates in the circumferential direction is
referred to as a rotation direction. In the example illustrated in
FIG. 2, the rotation direction indicates being counterclockwise,
but may indicates the opposite direction (clockwise).
[0022] In the example illustrated in FIG. 2, the disk 10 includes a
disk 10-0 and the like. The disk 10 has surfaces 10S (10S0, 10S1,
and the like). The disk 10-0 has a front surface 1050 and a back
surface 10S1 on the opposite side of the front surface 1050. The
surface 1050 has a user data region 10a0, a media cache 10b0, and a
system region 10c0. The back surface 1051 has a user data region
10a1, a media cache 10b1, and a system region 10c1.
[0023] In the example illustrated in FIG. 2, the head 15 includes a
head 15-0, a head 15-1, and the like. The head 15 faces the surface
10S. The head 15-0 faces the surface 1050. The head 15-0 writes
data onto the surface 1050 and reads data from the surface 1050.
The head 15-1 faces the back surface 10S1. The head 15-1 writes
data to the back surface 10S1 and reads data from the back surface
10S1. Three or more heads 15 and three or more disks 10 may be
provided.
[0024] FIG. 3 is an enlarged cross-sectional view illustrating an
example of the disk 10 and the head 15 according to the embodiment.
In FIG. 3, a rotation direction B of the disk 10 (10-0 and the
like) coincides with a direction of an air flow C. A direction from
the head 15 (15-0, 15-1, and the like) toward the disk 10 is
referred below to as a downward direction, or simply as being
downward. A direction from the disk 10 toward the head 15 is
referred below to as an upward direction or simply as being upward.
When expressions such as "another layer on a particular layer" and
"another layer under a particular layer" are used, the another
layer may be in contact with the particular layer or may be located
to be spaced from the particular layer.
[0025] In the example illustrated in FIG. 3, in the disk 10, a
substrate 111, a soft magnetic layer 112, a magnetic recording
layer 113, and a protective film layer 114 are stacked in this
order. The substrate 111 is formed of a disk-shaped nonmagnetic
material. The soft magnetic layer 112 is located on the substrate
111. The soft magnetic layer 112 is formed of a material exhibiting
soft magnetic properties. The magnetic recording layer 113 is
located on the soft magnetic layer 112. The magnetic recording
layer 113 has magnetic anisotropy in a direction perpendicular to
the front surface of the disk 10 (front surface of the magnetic
recording layer 113 or the front surface of the protective film
layer 114). The protective film layer 114 is located on the
magnetic recording layer 113.
[0026] In the example illustrated in FIG. 3, the head 15 includes a
slider 150. The slider 150 is formed of, for example, a sintered
body (artic) of alumina and titanium carbide. The slider 150 has a
front surface of the disk 10, for example, a disk facing surface
(air bearing surface (ABS)) 151 that faces the protective film
layer 114, and a trailing end 153 located on the outflow side of
the air flow C. A part of the read head 15R and the write head 15W
is exposed on the disk facing surface 151.
[0027] The read head 15R includes a magnetic film 161, a shield
film 162, and a shield film 163. The magnetic film 161 is located
between the shield film 162 and the shield film 163 and produces a
magnetoresistive effect. The shield film 162 is located on the
trailing end 153 side with respect to the magnetic film 161. The
shield film 163 faces the shield film 162. The lower ends of the
magnetic film 161, the shield film 162, and the shield film 163 are
exposed on the disk facing surface 151.
[0028] The write head 15W is provided on the trailing end 153 side
of the slider 150 with respect to the read head 15R. The write head
15W is comprised of a main magnetic pole 171, a trailing shield
(write shield) 172, an insulator 173, a recording coil 180, and a
magnetic flux control unit (assist element), for example, a spin
torque oscillator (STO) 200. The recording coil 180 is disposed to
be wound around a magnetic circuit including the main pole 171 and
the write shield 172 in order to allow magnetic flux to flow
through the main pole 171.
[0029] The main magnetic pole 171 is formed of a soft magnetic
material having high saturation magnetic flux density. The main
magnetic pole 171 generates a recording magnetic field in the
direction perpendicular to the front surface of the disk 10 in
order to magnetize the magnetic recording layer 113 of the disk 10.
In the example illustrated in FIG. 3, the main magnetic pole 171
extends substantially perpendicular to the disk facing surface 151.
The lower surface of a tip portion 171a of the main magnetic pole
171 on the disk facing surface 151 side is exposed on the disk
facing surface 151. The tip portion 171a of the main magnetic pole
171 is tapered toward the disk facing surface 151 and is formed in
a columnar shape having a width narrower than the other portions.
The width of the tip portion 171a of the main magnetic pole 171 in
a cross-track direction substantially corresponds to the track
width of a particular track. The cross-track direction is, for
example, a direction along the radial direction.
[0030] The write shield 172 is formed of a soft magnetic material
having high saturation magnetic flux density. The write shield 172
is provided to efficiently close a magnetic path via the soft
magnetic layer 112 directly below the main magnetic pole 171. The
write shield 172 is located on the trailing end 153 side with
respect to the main magnetic pole 171. The write shield 172 is
joined to the main magnetic pole 171 via the insulator 173. The
main magnetic pole 171 and the write shield 172 are electrically
insulated from each other and form the magnetic circuit. The write
shield 172 is formed in a substantially L shape, and has a tip
portion 172a facing the disk facing surface 151 with a write gap at
the tip portion 171a of the main magnetic pole 171. The lower
surface of the tip portion 172a is exposed on the disk facing
surface 151 of the slider 150.
[0031] The recording coil 180 is provided to wind around the
magnetic circuit including the main magnetic pole 171 and the write
shield 172 in order to allow magnetic flux to flow through the main
magnetic pole 171. The recording coil 180 is provided, for example,
between the main magnetic pole 171 and the write shield 172. When a
current (referred to as a write current or a recording current) of
a particular magnitude is supplied to the recording coil 180, a
recording magnetic field is excited in the main magnetic pole 171
and the write shield 172. Therefore, the main magnetic pole 171 and
the write shield 172 are magnetized. The magnetization direction of
a recording bit of the magnetic recording layer 113 in the disk 10
is changed by the magnetic flux flowing through the magnetized main
magnetic pole 171 and write shield 172. With the change of the
magnetization direction, a magnetization pattern corresponding to
the recording current is recorded on the disk 10.
[0032] The assist element, for example, the spin torque oscillator
(STO) 200, is provided between the tip portion 171a of the main
magnetic pole 171 and the tip portion 172a of the write shield 172.
In other words, the spin torque oscillator 200 is provided in the
write gap. For example, the STO 200 has a structure in which an
underlayer formed by a nonmagnetic conductive layer, a spin
injection layer, an intermediate layer, an oscillation layer, and a
gap layer formed by a nonmagnetic conductive layer are sequentially
stacked from the tip portion 171a side of the main magnetic pole
171 to the tip portion 172a side of the write shield 172.
[0033] The assist element, for example, the STO 200, generates
energy for improving the write performance of the write head 15W
into the disk 10, on the surface 10S (10S0, 10S1, and the like) of
the disk 10. The STO 200 generates a high-frequency (microwave)
magnetic field in a manner as follows. That is, for example,
particular energy (may be referred to as element energy), for
example, a particular current (referred to as a bias current, a
drive current, or an assist current) or a particular voltage
(referred to as a bias voltage, a drive voltage, or an assist
voltage) is applied to generate a gap magnetic field in the write
gap. With the gap magnetic field, the magnetization rotates
uniformly (spin precession motion), and thus the high-frequency
magnetic field having a frequency which is sufficiently higher than
the frequency of a recording signal is generated toward the disk
10. The STO 200 reduces the coercive force of the magnetic
recording layer 113 by applying a high-frequency magnetic field to
the magnetic recording layer 113 of the disk 10. When the spin
precession motion is largely generated in the spin torque
oscillator 200, the magnetic permeability of the STO 200 becomes as
low as the magnetic permeability of an air. Therefore, the magnetic
flux from the main magnetic pole 171 is more likely to flow toward
the disk 10 than the write gap (STO 200). When the spin precession
motion is not generated in the STO 200 or is generated smaller than
usual, the magnetic permeability of the spin torque oscillator 200
becomes higher than the magnetic permeability of the air.
Therefore, the magnetic flux from the main magnetic pole 171 is
more likely to flow toward the write gap (STO 200) than the disk
10. A write process of supplying element energy, for example, a
drive current (or may also be referred to as an assist current) or
a drive voltage (or may also be referred to as an assist voltage)
to the assist element, for example, the STO 200, to write data may
also be referred below to as assist recording or high frequency
assisted recording. The effect of assisting the write process into
the disk 10 may be referred below to as an assist effect. "Assisted
recording" may be simply referred to as "writing".
[0034] The driver IC 20 controls driving of the SPM 12 and the VCM
14 under control of the system controller 130 (specifically, MPU 60
described later).
[0035] The head amplifier IC (preamplifier) 30 includes a read
amplifier and a write driver (either not illustrated), for example,
a recording current control circuit 310, an element energy control
circuit 320, and the like. The read amplifier amplifies a read
signal read from the disk 10 and outputs the amplified signal to
the system controller 130 (specifically, read/write (R/W) channel
50 described later). The recording current control circuit 310 is
electrically connected to the recording coil 180 to supply the
recording current corresponding to write data output from the R/W
channel 50, to the recording coil 180. Data written into the disk
10 may be referred below to as write data, and data read from the
disk 10 may be referred below to as read data. For example, the
recording current control circuit 310 supplies the recording
current to the recording coil 180 under the control of the system
controller 130 (MPU 60). The element energy control circuit 320 is
electrically connected to the assist element, for example, the spin
torque oscillator 200. The element energy control circuit 320
applies particular element energy, for example, a particular assist
current or a particular assist voltage to the spin torque
oscillator 200 under the control of the system controller 130, for
example, the MPU 60. The element energy control circuit 320
measures the resistance value (may also be referred below to as an
assist-element resistance value) of the assist element, for
example, the spin torque oscillator 200.
[0036] The volatile memory 70 is a semiconductor memory in which
stored data is lost when the power is not supplied. The volatile
memory 70 stores data and the like required for processing in each
unit of the magnetic disk device 1. The volatile memory 70 is, for
example, a dynamic random access memory (DRAM) or a synchronous
dynamic random access memory (SDRAM).
[0037] The non-volatile memory 80 is a semiconductor memory that
records the stored data even though the power is not supplied. The
non-volatile memory 80 is, for example, a NOR type or NAND type
flash ROM (Flash Read Only Memory: FROM).
[0038] The buffer memory 90 is a semiconductor memory that
temporarily records data and the like which are transmitted and
received between the magnetic disk device 1 and a host 100. The
buffer memory 90 may be integrally configured with the volatile
memory 70. The buffer memory 90 is, for example, a DRAM, a static
random access memory (SRAM), an SDRAM, a ferroelectric random
access memory (FeRAM), a magnetoresistive random access memory
(MRAM), or the like.
[0039] The system controller (controller) 130 is realized, for
example, by using a large-scale integrated circuit (LSI) referred
to as a system-on-a-Chip (SoC) in which a plurality of elements are
integrated on a single chip. The system controller 130 includes a
hard disk controller (HDC) 40, the read/write (R/W) channel 50, and
the microprocessor (MPU) 60. The HDC 40, the R/W channel 50, and
the MPU 60 are electrically connected to each other. The system
controller 130 is electrically connected to, for example, the
driver IC 20, the head amplifier IC 60, the volatile memory 70, the
non-volatile memory 80, the buffer memory 90, the host system 100,
and the like.
[0040] The HDC 40 controls data transfer between the host 100 and
the R/W channel 50 in response to an instruction from the MPU 60
described later. The HDC 40 is electrically connected to, for
example, the volatile memory 70, the non-volatile memory 80, the
buffer memory 90, and the like.
[0041] The R/W channel 50 executes signal processing of read data
and write data in response to an instruction from the MPU 60. The
R/W channel 50 is electrically connected to, for example, the head
amplifier IC 30 or the like. The R/W channel 50 has a circuit or a
function of modulating write data. The R/W channel 50 has a circuit
or a function of measuring the signal quality of the read data.
[0042] The MPU 60 is a main controller that controls each unit in
the magnetic disk device 1. The MPU 60 controls the VCM 14 via the
driver IC 20 and performs positioning of the head 15. The MPU 60
controls a write operation of data into the disk 10 and selects the
storing destination of write data transferred from the host 100.
The MPU 60 controls read operation of data from the disk 10 and
controls processing of read data transferred from the disk 10 to
the host 100. The MPU 60 is connected to each unit of the magnetic
disk device 1. The MPU 60 is electrically connected to, for
example, the driver IC 20, the HDC 40, the R/W channel 50, and the
like.
[0043] The MPU 60 includes a read/write controller 610, an energy
controller 620, a resistance value measurement unit 630, a degauss
adjustment unit 640, and a format setting unit 650. The MPU 60
executes processing of each unit, for example, the read/write
controller 610, the energy controller 620, the resistance value
measurement unit 630, the degauss adjustment unit 640, the format
setting unit 650, or the like, on the firmware. The MPU 60 may
include each unit, for example, the read/write controller 610, the
energy controller 620, the resistance value measurement unit 630,
the degauss adjustment unit 640, the format setting unit 650, and
the like as a circuit.
[0044] The read/write controller 610 controls a write process and
read process of data in response to a command or the like from the
host 100 or the like. When the read/write controller 610 receives a
command from the host 100 or the like, the read/write controller
executes the write process of writing data into a particular
region. When the read/write controller 610 receives a command from
the host 100 or the like, the read/write controller executes the
read process of reading data from a particular region. The
read/write controller 610 controls the VCM 14 via the driver IC 20,
performs positioning of the head 15 at a target position on the
disk 10, and executes the write process or the read process. For
example, the read/write controller 610 supplies a recording current
to the recording coil 180 to excite a recording magnetic field in
the main magnetic pole 171 and the write shield 172. Then, the
read/write controller 610 supplies element energy, for example, the
assist current or the assist voltage to the assist element, for
example, the STO 200, to generate a high-frequency magnetic field.
Thus, data is written (assisted recording) into a particular region
of the disk 10. The read/write controller 610 may supply the
recording current to the recording coil 180 to excite the recording
time to the main magnetic pole 171 and the write shield 172. Then,
the read/write controller may not supply the element energy, for
example, the assist current or the assist voltage to the assist
element, for example, the STO 200. Thus, data may be written into a
particular region of the disk 10 without the assist effect. For
example, the read/write controller 610 temporarily stops the write
process of data into a particular region of a particular track, for
example, into a region immediately before servo data (or tip
portion of the servo data), to read the servo data. Then, the
read/write controller 610 starts the write process of data from a
region immediately after the servo data (or rear end portion on an
opposite side of the tip portion of the servo data) again to write
data. The read/write controller 610 temporarily stops the write
process of data into a region immediately before a particular
region of a particular track (or tip portion of this region) and
executes degauss until the read process of the servo data is
started. The degauss (may also be referred below to as a degauss
operation or a degauss process) means, for example, processing of
gradually attenuating the recording current (or recording voltage)
to be supplied to the recording coil 180 from the recording current
control circuit 310 of the head amplifier IC 30 when the write
process is stopped, and gradually eliminating the residual
magnetization generated in the write head 15W (main magnetic pole
171 and write shield 172) in accordance with the shape of the head
15. A period until the recording current (or recording voltage)
reaches a particular value, for example, 0 after the write process
is stopped, or until the magnetization generated in the main
magnetic pole 171 and the write shield 172, for example, the
residual magnetization disappears after the write process is
stopped may also be referred to as a degauss duration. The
frequency of the recording current (or recording voltage) during
the degauss duration may be referred to as a degauss frequency. In
the degauss operation in accordance with a degauss condition
including the set degauss duration and degauss frequency, the
read/write controller 610 may write not-desired data or meaningless
data into a region (may be referred to as a degauss region below)
adjacent to a region immediately before servo data, for example,
into Gap (may be referred to as a previous Gap below) adjacent to
the region immediately before the servo data. Such writing of
not-desired data or meaningless data is caused by the residual
magnetization generated in the head 15 (write head 15W) during a
period from when the write process of data is stopped in a
particular region, for example, in a region immediately before the
servo data until the read process of the servo data is started.
Here, "being adjacent" includes not only a case where data, an
object, a region, a space, and the like are arranged in contact
with each other, but also a case where data, an object, a region, a
space, and the like are arranged at a particular interval.
[0045] FIG. 4 is a schematic diagram illustrating an example of the
degauss operation. In FIG. 4, a horizontal axis indicates time. On
the horizontal axis in FIG. 4, the time elapses as directing toward
the tip of an arrow. Timings T41 and T42 are shown on the
horizontal axis in FIG. 4. A timing T42 corresponds to a timing
after a timing T41. FIG. 4 illustrates a write gate WG, the
recording current, and a track TRex. In the write gate WG of FIG.
4, a signal level L indicates that the write gate is in the negate
(inactive, disabled, or OFF) state. A signal level H indicates that
the write gate is asserted (active, enabled, or ON) state. The
write gate WG has the signal level L from the signal level H to at
the timing T41. The recording current in FIG. 4 indicates a current
value C0. The current value C0 is a constant value, for example, 0.
In FIG. 4, the track TRex has user data (may be referred to as
previous user data below) located before the servo data, a previous
Gap (gap), and servo data. In the track TRex of FIG. 4, the
previous user data, the previous Gap (gap), and the servo data are
arranged in the order described. In other words, the previous Gap
is disposed between the previous user data and the servo data.
[0046] In the example illustrated in FIG. 4, the read/write
controller 610 negates the write gate WG at the circumferential
position in the previous Gap, which corresponds to the timing T41,
so as to stop the write process. In the degauss operation in
accordance with the set degauss duration and the set degauss
frequency, the read/write controller 610 may write data
corresponding to the residual magnetization of the head 15 based on
the recording current having the degauss frequency in a range of
the previous Gap from the circumferential position in the previous
Gap, which corresponds to the timing T41 to the circumferential
position in the previous Gap, which corresponds to the timing
T42.
[0047] The energy controller 620 controls (or adjusts) the energy
to be supplied to the head 15. The energy controller 620 controls
(or adjusts) the recording current to be supplied (or applied) to
the recording coil 180 and the element energy to be supplied (or
applied) to the assist element. For example, the energy controller
620 controls (or adjusts) the element energy, for example, the
assist current or the assist voltage to be supplied (or applied) to
the assist element, for example, the STO 200.
[0048] The resistance value measurement unit 630 measures the
resistance value of each unit of the head 15. The resistance value
measurement unit 630 measures the assist-element resistance value
of the assist element, for example, the STO 200. For example, the
resistance value measurement unit 630 measures the assist-element
resistance value of the assist element, for example, the STO 200,
via the element energy control circuit 320 of the head amplifier IC
30. The resistance value measurement unit 630 measures the
assist-element resistance value of the assist element, for example,
the STO 200, after data is written into a particular region of the
disk 10 and then the write process is stopped. "After data is
written into a particular region of the disk 10 and then the write
process is stopped" may be simply referred to as "after writing" or
"after write". The assist-element resistance value may change, for
example, depending on the magnetization state of the write head 15W
(main magnetic pole 171 and write shield 172). In other words, the
assist-element resistance value may be affected by the degauss
operation in accordance with the degauss condition. That is, the
assist element and the degauss condition may influence each other.
For example, since the assist-element resistance value is measured
after data is written into a particular region, it is possible to
check the magnetization (for example, residual magnetization) state
between the main magnetic pole 171 and the write shield 172 after
writing. In other words, it is possible to check the influence of
the degauss condition by measuring the assist-element resistance
value after the data is written into the particular region. That
is, it is possible to estimate whether or not the degauss condition
is the optimum, by measuring the assist-element resistance value
after write.
[0049] The degauss adjustment unit 640 adjusts (changes or sets)
the degauss condition such as the degauss duration and the degauss
frequency corresponding to the head 15. The degauss adjustment unit
640 adjusts the degauss condition corresponding to the head 15, in
accordance with the assist-element resistance value corresponding
to the head 15. The degauss adjustment unit 640 adjusts the degauss
condition corresponding to the head 15 so that fluctuation in the
assist-element resistance value is small when measurement of the
assist-element resistance value corresponding to the head 15 after
the head 15 writes data into a particular region (may also be
simply referred below to as measurement of the assist-element
resistance value corresponding to the head 15) is performed a
particular number of times (may also be referred to as the number
of resistance value measurements below). Since the assist-element
resistance value may change depending on the characteristics of the
head 15, the degauss adjustment unit 640 may set the degauss
condition to differ for each head 15. The degauss adjustment unit
640 may set the degauss condition to be the same for a plurality of
heads 15.
[0050] For example, when the assist-element resistance value
corresponding to the head 15 is out of a range of Thr_upper and
Thr_lower, the degauss adjustment unit 640 adjusts the degauss
condition corresponding to the head 15 so that the assist-element
resistance value corresponding to the head 15 is within the range
of Thr_upper being the resistance upper limit value corresponding
to the head 15 and Thr_lower being the resistance lower limit value
corresponding to the head 15. Thr_upper indicates the upper limit
(may be also referred to as a resistance upper limit value below)
of the assist-element resistance value corresponding to the head
15. Thr_lower indicates the lower limit (may be also referred to as
a resistance lower limit value below) of the assist-element
resistance value corresponding to the head 15. When the
assist-element resistance value corresponding to the head 15 is out
of a range of Thr_upper indicating the upper limit (may be also
referred to as a resistance upper limit value below) of the
assist-element resistance value corresponding to the head 15 and
Thr_lower indicating the lower limit (may be also referred to as a
resistance lower limit value below) of the assist-element
resistance value corresponding to the head 15, the degauss
adjustment unit 640 may adjust the degauss duration corresponding
to the head 15 to increase and/or adjust the degauss frequency to
increase. When the assist-element resistance value corresponding to
the head 15 is out of a range of Thr_upper indicating the upper
limit (may be also referred to as a resistance upper limit value
below) of the assist-element resistance value corresponding to the
head 15 and Thr_lower indicating the lower limit (may be also
referred to as a resistance lower limit value below) of the
assist-element resistance value corresponding to the head 15, the
degauss adjustment unit 640 may adjust the degauss duration
corresponding to the head 15 to increase and/or adjust the degauss
frequency to decrease. When the assist-element resistance value
corresponding to the head 15 is out of a range of Thr_upper
indicating the upper limit (may be also referred to as a resistance
upper limit value below) of the assist-element resistance value
corresponding to the head 15 and Thr_lower indicating the lower
limit (may be also referred to as a resistance lower limit value
below) of the assist-element resistance value corresponding to the
head 15, the degauss adjustment unit 640 may adjust the degauss
duration corresponding to the head 15 to decrease and/or adjust the
degauss frequency to increase. When the assist-element resistance
value corresponding to the head 15 is out of a range of Thr_upper
indicating the upper limit (may be also referred to as a resistance
upper limit value below) of the assist-element resistance value
corresponding to the head 15 and Thr_lower indicating the lower
limit (may be also referred to as a resistance lower limit value
below) of the assist-element resistance value corresponding to the
head 15, the degauss adjustment unit 640 may adjust the degauss
duration corresponding to the head 15 to decrease and/or adjust the
degauss frequency to decrease.
[0051] For example, when the assist-element resistance value
corresponding to the head 15 is within the range of Thr_upper
indicating the resistance upper limit value corresponding to the
head 15 and Thr_lower indicating the resistance lower limit value
corresponding to the head 15, the degauss adjustment unit 640
maintains the degauss condition corresponding to the head 15. For
example, when the assist-element resistance value corresponding to
the head 15 is within the range of Thr_upper indicating the
resistance upper limit value corresponding to the head 15 and
Thr_lower indicating the resistance lower limit value corresponding
to the head 15, the degauss adjustment unit 640 may adjust the
degauss condition corresponding to the head 15 so that the
fluctuation in the assist-element resistance value when the
measurement of the assist-element resistance value corresponding to
the head 15 is performed the number of times corresponding to the
number of resistance value measurements is further reduced.
[0052] For example, the degauss adjustment unit 640 sets the number
of resistance value measurements for measuring the assist-element
resistance value corresponding to the head 15, and sets Thr_upper
indicating the resistance upper limit value of the assist-element
resistance value corresponding to the head 15 and Thr_lower
indicating the resistance lower limit value of the assist-element
resistance value corresponding to the head 15. The degauss
adjustment unit 640 initializes the number of times of writing data
into a particular area of the disk 10 by the head 15 (may be
referred to as the number of writes), for example, sets the number
of times to 0. Then, the degauss adjustment unit repeats to write
data into this region until the counter value reaches the number of
resistance value measurements, while counting the number of times
of writing data into the region. Each time data is written in the
region by the head 15, the degauss adjustment unit 640 measures the
assist-element resistance value corresponding to the head 15 after
the head 15 writes data into the region, and records the measured
assist-element resistance value after the write, in a particular
recording region, for example, the system region 10c of the disk
10, the volatile memory 70, the non-volatile memory 80, the buffer
memory 90, and the like. The degauss adjustment unit 640 calculates
the average value (RSV_Ave) of the assist-element resistance value
when the assist-element resistance value corresponding to the head
15 is measured the number of times corresponding to the number of
resistance value measurements. The degauss adjustment unit 640
detects the minimum value (RSV_min) of the assist-element
resistance value when the assist-element resistance value
corresponding to the head 15 is measured the number of times
corresponding to the number of resistance value measurements, and
detects the maximum value (RSV_max) of the assist-element
resistance value when the assist-element resistance value
corresponding to the head 15 is measured the number of times
corresponding to the number of resistance value measurements. "The
minimum value of the assist-element resistance value when the
assist-element resistance value corresponding to the head 15 is
measured the number of times corresponding to the number of
resistance value measurements" may also be simply referred to as
"the minimum value of the assist-element resistance value" below.
"The maximum value of the assist-element resistance value when the
assist-element resistance value corresponding to the head 15 is
measured the number of times corresponding to the number of
resistance value measurements" may also be simply referred to as
"the maximum value of the assist-element resistance value" below.
The degauss adjustment unit 640 determines whether the minimum
value of the assist-element resistance value/the average value of
the assist-element resistance value<the resistance lower limit
value, or the minimum value of the assist-element resistance
value/the average value of the assist-element resistance value the
resistance lower limit value. When the degauss adjustment unit 640
determines that the minimum value of the assist-element resistance
value/the average value of the assist-element resistance
value<the resistance lower limit value, the degauss adjustment
unit 640 adjusts (changes) the degauss condition. The degauss
adjustment unit 640 determines whether the maximum value of the
assist-element resistance value/the average value of the
assist-element resistance value>the resistance upper limit
value, or the maximum value of the assist-element resistance
value/the average value of the assist-element resistance value the
resistance upper limit value. When the degauss adjustment unit 640
determines that the maximum value of the assist-element resistance
value/the average value of the assist-element resistance
value>the resistance upper limit value, the degauss adjustment
unit 640 adjusts (changes) the degauss condition.
[0053] FIG. 5 is a schematic view illustrating another example of
the method of adjusting the degauss condition corresponding to the
head 15-0 according to the present embodiment. In FIG. 5, a
vertical axis indicates the assist-element resistance value
[.OMEGA.] corresponding to the head 15-0, and a horizontal axis
indicates the number of times of the head 15-0 performing writing
into a particular region on the surface 1050 of the disk 10-0. On
the vertical axis in FIG. 5, the assist-element resistance value
increases toward the tip of a large arrow and decreases toward the
tip of a small arrow. On the vertical axis in FIG. 5, the average
value RSV_Ave0 of the assist-element resistance value corresponding
to the head 15-0, the resistance upper limit value Thr_upper0
corresponding to the head 15-0, and the resistance lower limit
value Thr_lower0 corresponding to the head 15-0 are shown. On the
horizontal axis in FIG. 5, the number of writes increases toward
the tip of an arrow. FIG. 5 illustrates RSV_0 being a change (may
also be referred to as a change in the assist-element resistance
value below) of the assist-element resistance value corresponding
to the head 15-0 with respect to the number of writes. The change
RSV_0 in the assist-element resistance value corresponding to the
head 15-0 is within a range of the resistance upper limit value
Thr_upper0 and the resistance lower limit value Thr_lower0.
[0054] In the example illustrated in FIG. 5, when the change RSV_0
in the assist-element resistance value corresponding to the head
15-0 is within the range of Thr_upper0 indicating the resistance
upper limit value corresponding to the head 15-0 and Thr_lower0
indicating the resistance lower limit value corresponding to the
head 15-0, the degauss adjustment unit 640 maintains the degauss
condition corresponding to the head 15.
[0055] FIG. 6 is a schematic view illustrating an example of the
method of adjusting the degauss condition corresponding to the head
15-1 according to the present embodiment. In FIG. 6, a vertical
axis indicates the assist-element resistance value [.OMEGA.]
corresponding to the head 15-1, and a horizontal axis indicates the
number of times of the head 15-1 performing writing into a
particular region on the surface 10S1 of the disk 10-0. On the
vertical axis in FIG. 6, the assist-element resistance value
increases toward the tip of a large arrow and decreases toward the
tip of a small arrow. On the vertical axis in FIG. 6, the average
value RSV_Ave1 of the assist-element resistance value corresponding
to the head 15-1, the resistance upper limit value Thr_upper1
corresponding to the head 15-1, and the resistance lower limit
value Thr_lower1 corresponding to the head 15-1 are shown. On the
horizontal axis in FIG. 6, the number of writes increases toward
the tip of an arrow. FIG. 6 illustrates RSV_1 being a change (may
also be referred to as a change in the assist-element resistance
value below) of the assist-element resistance value corresponding
to the head 15-1 with respect to the number of writes. The change
RSV_1 in the assist-element resistance value corresponding to the
head 15-1 is within a range of the resistance upper limit value
Thr_upper1 and the resistance lower limit value Thr_lower1.
[0056] In the example illustrated in FIG. 6, when the change RSV_1
in the assist-element resistance value corresponding to the head
15-1 is out of the range of Thr_upper1 indicating the resistance
upper limit value of the assist-element resistance value
corresponding to the head 15-1 and Thr_lower1 indicating the
resistance lower limit value of the assist-element resistance value
corresponding to the head 15-1, the degauss adjustment unit 640
adjusts the degauss condition corresponding to the head 15-1 so
that the change RSV 1 in the assist-element resistance value
corresponding to the head 15 is within the range of Thr_upper1
indicating the resistance upper limit value of the assist-element
resistance value corresponding to the head 15-1 and Thr_lower1
indicating the resistance lower limit value of the assist-element
resistance value corresponding to the head 15-1.
[0057] The format setting unit 650 adjusts the data format (may be
simply referred to as a format below) of the disk 10 with which the
head 15 faces, in accordance with the degauss condition
corresponding to the head 15. The format setting unit 650 sets the
length (length of the degauss region or length of the previous Gap
below) of the degauss region (or previous Gap) of the disk 10,
which face the head 15, in the circumferential direction or sets
the size of the degauss region, in accordance with the degauss
condition corresponding to the head 15. When the different degauss
condition is set for each head 15, the format setting unit 650 may
set a degauss region having a different degauss region length or
having a different size, for each surface 10S of the disk 10, which
faces the head 15. When the different degauss condition is set for
each head 15, the format setting unit 650 may set a degauss region
having the same degauss region length or having the same size, for
each surface 10S of the disk 10, which faces the head 15. When the
same degauss condition is set for each head 15, the format setting
unit 650 may set a degauss region having a different degauss region
length or having a different size, for each surface 10S of the disk
10, which faces the head 15. In addition, when the same degauss
condition is set for each head 15, the format setting unit 650 may
set a degauss region having the same degauss region length or
having the same size, for each surface 10S of the disk 10, which
faces the head 15.
[0058] When the degauss condition which corresponds to the head 15
and is adjusted based on the assist-element resistance value
corresponding to the head 15 is larger than the degauss condition
set as the reference in the initial setting and the like (may be
referred to as a reference degauss condition below), for example,
the degauss duration as a reference (may be referred to as a
reference degauss duration below) and the degauss frequency as a
reference (may be referred to as a reference degauss frequency
below), the format setting unit 650 may set the degauss region
length of the degauss region of the disk 10 corresponding to the
head 15 to be longer than the degauss region length or the degauss
region as a reference set in the initial setting and the like in
the disk 10. When the degauss condition corresponding to the head
15 is smaller than the reference degauss condition (reference
degauss duration and reference degauss frequency) set based on the
assist-element resistance value corresponding to the head 15 in the
initial setting or the like, the format setting unit 650 may set
the degauss region length of the degauss region of the disk 10
corresponding to the head 15 to be shorter than the reference
degauss region length set in the initial setting and the like in
the disk 10. For example, when the degauss condition corresponding
to the head 15 is the same as the reference degauss condition set
in the initial setting or the like, the format setting unit 650 may
maintain the degauss region length of the degauss area of the disk
10 corresponding to the head 15.
[0059] FIG. 7 is a schematic view illustrating an example of a
format of the front surface 1050 of the disk 10-0 corresponding to
the head 15-0 according to the present embodiment. In FIG. 7, a
horizontal axis indicates time. On the horizontal axis in FIG. 7,
the time elapses as directing toward the tip of an arrow. The
horizontal axis in FIG. 7 shows timings T71, T72, T73, T74, and
T75. The timing T72 corresponds to a timing after the timing T71.
The timing T73 corresponds to a timing after the timing T72. The
timing T74 corresponds to a timing after the timing T73. The timing
T75 corresponds to a timing after the timing T74. FIG. 7
illustrates the write gate WG and the track TR0 on the front
surface 1050 of the disk 10. In FIG. 7, the track TR0 has the
previous user data, the previous Gap (degauss region), the servo
data, the adjacent Gap immediately after the servo data (may also
be referred to as the subsequent Gap below), and user data located
after the servo data (may also be referred to as subsequent user
data below). In the track TR0 of FIG. 7, the previous user data,
the previous Gap (degauss region), the servo data, the subsequent
Gap, and the subsequent user data are arranged in the order
described. The subsequent Gap is disposed between the servo data
and the subsequent user data. FIG. 7 illustrates the length
(degauss region length) L71 of the previous Gap, the length (may
also be referred to as the length of the servo data below) SDL of
the servo data in the circumferential direction, and the length
(may also be referred to as the length of the subsequent Gap below)
GPL of the subsequent Gap in the circumferential direction. The
length (degauss region length) L71 of the previous Gap corresponds
to the length in the circumferential direction, from the
circumferential position corresponding to the timing T71 to the
circumferential position corresponding to the timing T73. The
length SDL of the servo data corresponds to the length in the
circumferential direction, from the circumferential position
corresponding to the timing T73 to the circumferential position
corresponding to the timing T74. The length GPL of the subsequent
Gap corresponds to the length in the circumferential direction,
from the circumferential position corresponding to the timing T74
to the circumferential position corresponding to the timing T75.
For example, the length L71 of the previous Gap is smaller than the
reference degauss region length. FIG. 7 illustrates a degauss
duration DD71 adjusted based on the change RSV 0 of the assist
resistance value illustrated in FIG. 5. The degauss duration DD71
corresponds to the period from the timing T71 to the timing T72.
For example, the degauss duration DD71 is shorter than the
reference degauss duration.
[0060] In the example illustrated in FIG. 7, when the format
setting unit 650 determines that the degauss duration DD71 adjusted
based on the change RSV 0 of the assist resistance value
illustrated in FIG. 5 is shorter than the reference degauss
duration, the format setting unit sets the length of the previous
Gap to be the degauss region length L71 which is shorter than the
reference degauss length.
[0061] The read/write controller 610 negates the write gate WG at
the circumferential position in the previous Gap, which corresponds
to the timing T71, so as to stop the write process. In the degauss
operation in accordance with the degauss duration DD71, the
read/write controller 610 writes data corresponding to the residual
magnetization of the head 15-0 in a range in the previous Gap from
the circumferential position in the previous Gap corresponding to
the timing T71 to the circumferential position in the previous Gap
corresponding to the timing T72. The read/write controller 610
reads the servo data from the circumferential position in the servo
data corresponding to the timing T73 to the circumferential
position in the servo data corresponding to the timing T74. The
read/write controller 610 asserts the write gate WG at the
circumferential position in the subsequent user data corresponding
to the timing T75 so as to start (restart) the write process.
[0062] FIG. 8 is a schematic view illustrating an example of a
format of the back surface 10S1 of the disk 10-0 corresponding to
the head 15-1 according to the present embodiment. In FIG. 8, a
horizontal axis indicates time. On the horizontal axis in FIG. 8,
the time elapses as directing toward the tip of an arrow. The
horizontal axis in FIG. 8 shows timings T81, T82, T83, T84, and
T85. The timing T82 corresponds to a timing after the timing T81.
The timing T83 corresponds to a timing after the timing T82. The
timing T84 corresponds to a timing after the timing T83. The timing
T85 corresponds to a timing after the timing T84. FIG. 8
illustrates the write gate WG and the track TR1 on the back surface
10S1 of the disk 10. In FIG. 8, the track TR1 has the previous user
data, the previous Gap (degauss region), servo data, the subsequent
Gap, and the subsequent user data. In the track TR1 of FIG. 8, the
previous user data, the previous Gap (degauss region), the servo
data, the subsequent Gap, and the subsequent user data are arranged
in the order described. FIG. 8 illustrates the length (degauss
region length) L81 of the previous Gap, the length SDL of the servo
data, and the length GPL of the subsequent Gap. The length (degauss
region length) L81 of the previous Gap corresponds to the length in
the circumferential direction, from the circumferential position
corresponding to the timing T81 to the circumferential position
corresponding to the timing T83. The length SDL of the servo data
corresponds to the length in the circumferential direction, from
the circumferential position corresponding to the timing T83 to the
circumferential position corresponding to the timing T84. The
length GPL of the subsequent Gap corresponds to the length in the
circumferential direction, from the circumferential position
corresponding to the timing T84 to the circumferential position
corresponding to the timing T85. For example, the length L81 of the
previous Gap is longer than the length L71 of the previous Gap
illustrated in FIG. 7. For example, the length L81 of the previous
Gap is longer than the reference degauss region length. FIG. 8
illustrates a degauss duration DD81 adjusted based on the change
RSV 1 of the assist resistance value illustrated in FIG. 6. The
degauss duration DD81 corresponds to the period from the timing T81
to the timing T82. For example, the degauss duration DD81 is longer
than the degauss duration DD71 illustrated in FIG. 7. For example,
the degauss duration DD81 is shorter than the reference degauss
duration.
[0063] In the example illustrated in FIG. 8, when the format
setting unit 650 determines that the degauss duration DD81 adjusted
based on the change RSV 1 of the assist resistance value
illustrated in FIG. 6 is longer than the reference degauss
duration, the format setting unit sets the length of the previous
Gap to be the degauss region length L81 which is longer than the
reference degauss length.
[0064] The read/write controller 610 negates the write gate WG at
the circumferential position in the previous Gap, which corresponds
to the timing T81, so as to stop the write process. In the degauss
operation in accordance with the degauss duration DD81, the
read/write controller 610 writes data corresponding to the residual
magnetization of the head 15-1 in a range in the previous Gap from
the circumferential position in the previous Gap corresponding to
the timing T81 to the circumferential position in the previous Gap
corresponding to the timing T82. The read/write controller 610
reads the servo data from the circumferential position in the servo
data corresponding to the timing T83 to the circumferential
position in the servo data corresponding to the timing T84. The
read/write controller 610 asserts the write gate WG at the
circumferential position in the subsequent user data corresponding
to the timing T85 so as to start (restart) the write process.
[0065] FIG. 9 is a flowchart illustrating an example of the method
of setting the data format according to the present embodiment.
[0066] The MPU 60 sets the number (N) of resistance value
measurements for measuring the assist-element resistance value
corresponding to the head 15 (B901). The MPU 60 sets Thr_upper
indicating the resistance upper limit value of the assist-element
resistance value corresponding to the head 15 and Thr_lower
indicating the resistance lower limit value of the assist-element
resistance value corresponding to the head 15 (B902). The MPU 60
initializes the number of times of the head 15 performing writing
into a particular region of the disk 10 (n=0) (B903), and executes
the write process in this region (B904). After executing the write
process in this region, the MPU 60 measures the assist-element
resistance value corresponding to the head 15 (B905). The MPU 60
sets the measured assist-element resistance value corresponding to
the head 15, in a particular recording region, for example, the
system region 10c of the disk 10, the volatile memory 70, the
non-volatile memory 80, the buffer memory 90, and the like (B906).
The MPU 60 adds 1 to the number of writes (n) and then determines
whether the number of writes (n) is more than the number (N) of
resistance value measurements or the number of writes (n) is equal
to or less than the number (N) of resistance value measurements
(B907). When the MPU determines that the number of writes (n) is
equal to or less than the number (N) of resistance value
measurements (NO in B907), the MPU 60 proceeds to the process of
B904. When the MPU determines that the number of writes (n) is more
than the number (N) of resistance value measurements (YES in B907),
the MPU 60 calculates the average value (RSV_Ave) of the
assist-element resistance value when the assist-element resistance
value corresponding to the head 15 is measured the number of times
corresponding to the number of resistance value measurements. The
MPU detects the minimum value (RSV_min) of the assist-element
resistance value when the assist-element resistance value
corresponding to the head 15 is measured the number of times
corresponding to the number of resistance value measurements. Then,
the MPU detects the maximum value (RSV_max) of the assist-element
resistance value when the assist-element resistance value
corresponding to the head 15 is measured the number of times
corresponding to the number of resistance value measurements
(B908).
[0067] The MPU 60 determines whether RSV_min/RSV_Ave<Thr_lower
or RSV_min/RSV_Ave.gtoreq.Thr_lower (B909). When the MPU determines
that RSV_min/RSV_Ave<Thr_lower (Yes in B909), the MPU 60 changes
the degauss condition (B910) and proceeds to the process of B903.
For example, the MPU 60 changes the degauss condition so that
RSV_min/RSV_Ave.gtoreq.Thr_lower and/or
RSV_max/RSV_Ave.ltoreq.Thr_upper.
[0068] When the MPU determines that
RSV_min/RSV_Ave.gtoreq.Thr_lower (No in B909), the MPU 60
determines whether RSV_max/RSV_Ave>Thr_upper or
RSV_max/RSV_Ave.ltoreq.Thr_upper (B911). When the MPU determines
that RSV_max/RSV_Ave>Thr_upper (Yes in B911), the MPU 60
proceeds to the process of B910. When the MPU determines that
RSV_max/RSV_Ave.ltoreq.Thr_upper (No in B911), the MPU 60 sets the
data format of the disk 10 with which the head 15 faces, in
accordance with the degauss condition corresponding to the head 15
(B912). Then, the MPU ends the processing. For example, the MPU 60
adjusts the degauss region length of the degauss region in a
particular track of the disk 10, with which the head 15 faces, in
accordance with the degauss condition corresponding to the head
15.
[0069] According to the present embodiment, the magnetic disk
device 1 adjusts the degauss condition corresponding to the head 15
so that the fluctuation of the assist-element resistance value when
the assist-element resistance value corresponding to the head 15 is
measured the number of times corresponding to the number of
resistance value measurements is reduced. For example, the magnetic
disk device 1 adjusts the degauss region length of the degauss
region in a particular track on the surface 10S of the disk 10 with
which the head 15 faces, in accordance with the adjusted degauss
condition. The magnetic disk device 1 can expand the user data
region of the disk 10 while avoiding pole erase of erasing data,
for example, servo data by the residual magnetization generated in
the write head 15W (main magnetic pole 171 and write shield 172)
after stopping the write process by adjusting the degauss region as
described above. Therefore, the magnetic disk device 1 can improve
the format efficiency.
[0070] In the above-described embodiment, the magnetic disk device
of the high frequency (microwave) assisted magnetic recording type
(MAMR) is described. The above-described embodiment can be applied
to the magnetic disk device of the thermally assisted magnetic
recording (TAMR) type when there is a part at which the resistance
value can be measured at the position affected by the recording
magnetic field.
[0071] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
embodiments described herein may be embodied in a variety of other
forms; furthermore, various omissions, substitutions and changes in
the form of the embodiments described herein may be made without
departing from the spirit of the inventions. The accompanying
claims and their equivalents are intended to cover such forms or
modifications as would fall within the scope and spirit of the
inventions.
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